Assessment of the performance of ECC‐ozonesondes under quasi‐flight conditions in the environmental simulation chamber: Insights from the Juelich Ozone Sonde Intercomparison Experiment (JOSIE)

Abstract

[1] Since 1996, quality assurance experiments of electrochemical concentration cell (ECC) ozonesondes of two different model types (SPC-6A and ENSCI-Z) have been conducted in the environmental simulation facility at the Research Centre Juelich within the framework of the Juelich Ozone Sonde Intercomparison Experiment (JOSIE). The experiments have shown that the performance characteristics of the two ECC-sonde types can be significantly different, even when operated under the same conditions. Particularly above 20 km the ENSCI-Z sonde tends to measure 5-10% more ozone than the SPC-6A sonde. Below 20 km the differences are 5% or less, but appear to show some differences with year of manufacture. There is a significant difference in the ozone readings when sondes of the same type are operated with different cathode sensing solutions. Testing the most commonly used sensing solutions showed that for each ECCmanufacturer type the use of 1.0% KI and full buffer gives 5% larger ozone values compared with the use of 0.5% KI and half buffer, and as much as 10% larger values compared with 2.0% KI and no buffer. For ozone sounding stations performing long term measurements this means that changing the sensing solution type or ECC-sonde type can easily introduce a change of ±5% or more in their records, affecting determination of ozone trends. Standardization of operating procedures for ECC-sondes yields a precision better than ±(3-5)% and an accuracy of about ±(5-10)% up to 30 km altitude.Citation: Smit, H. G. J., et al. (2007), Assessment of the performance of ECC-ozonesondes under quasi-flight conditions in the environmental simulation chamber:

On instrumental errors and related correction strategies of ozonesondes: possible effect on calculated ozone trends for the nearby sites Uccle and De Bilt

“…This BGC can be assumed constant during the flight, equal to 0 for BM sondes, or, alternatively, a pressure-dependent BGC correction can be used 2 , assuming a small oxygen dependence with a gradual decline that is proportional to decreasing pressure and is negligible in the upper troposphere and stratosphere (Komhyr, 1986). In this latter case, the BGC is assumed to be caused by a small interference of oxygen reacting with KI in the cathode and therefore generating a small additional current (Smit et al, 2007).…”

“…Although both ozonesonde stations used different ECC ozonesonde types, they both consistently stuck to the manufacturer's recommended SSTs, 0.5 % and 1 % KI for ENSCI Z (Uccle) and SPC (De Bilt), respectively. Therefore, the response of both ozonesondes should be very similar, as assessed in an environmental simulation chamber (Smit et al, 2007) and on a balloon experiment (Deshler et al, 2008). It should, however, be noted that the amount of the sensing so- lution at De Bilt changed from 2.5 to 3.0 cc on 23 November, 1994.…”

“…In 2011 ENSCI was taken over by Droplet Measurement Technologies (DMT). These two types of ECC sondes only have minor differences in construction and differences in recommended sensing solution strength (SST) and of its phosphate buffer (Smit et al, 2007;Deshler et al, 2008). For the BM and the ECC sondes, the principle of operation is based on the chemical titration of O 3 in a potassium iodide (KI) sensing solution.…”

“…Overall, the conversion efficiency is the predominant uncertainty at Uccle (≈ 3.6 % or the square root of the sum of the squares of the relative uncertainties of the absorption efficiency α O 3 and the stoichiometry S O 3 /I 2 , which are, respectively, 0.02 and 0.03,; see Smit et al, 2012), and the background current (BGC) has the largest influence on the overall uncertainty at the lowest O 3 concentrations in the upper troposphere. Unfortunately, the physicochemical origin of the BGC is not well understood and further research is required to better understand its origin and its appropriate measurement and treatment (Smit et al, 2007;Vömel and Diaz, 2010;Smit and the Panel for ASOPOS, 2011). The pump efficiency uncertainty contributes significantly to the overall uncertainty at altitudes starting from the ozone maximum, which, in altitudes relative to the tropopause, is in Uccle, located around 10-15 km (Fig.…”

Initial validation of ozone measurements from the High Resolution Dynamics Limb Sounder

“…[15] There is a certain amount of variability associated with use of ozonesondes, as each sonde is a unique instrument, especially when station-dependent factors are considered [Thompson et al, 2003a[Thompson et al, , 2003b[Thompson et al, , 2007Liu et al, 2006;Logan et al, 1999]. Among the conditions that factor into this variability are (1) the manufacturer of the instrument used (ENSCI-Corporation sondes can read 5 -10% higher than sondes from Science Pump Corporation (SPC), above 20 km [Thompson et al, 2007;Smit et al, 2007]); (2) the concentration of potassium iodide (KI) sensing cathode solution used, and whether or not it includes a buffering agent may also produce variances of 15% above the partial pressure layer peak [Johnson et al, 2002]; and (3) whether and how pump efficiency correction factors are implemented, which may also cause differences of up to 15% at upper altitudes [Johnson et al, 2002].…”